The present invention relates to air monitors and more particularly to air monitors of the type that may be worn or otherwise carried by an individual person (i.e. a personal air monitor) working or otherwise present in an environment where there is a hazard of exposure to certain toxic gases.
Devices have been developed that monitor the air to which a person is exposed in order to detect the presence of one or more certain hazardous gases in the environment in which the person is working. Devices of this type combine the operations of detecting a concentration of the hazardous gas that exceeds a predetermined threshold level and alerting the person about the detection of the gas. In order to perform these operations, the device must first necessarily obtain a representative sample of the air, detect the presence of one or more certain gases (i.e. target gases) in the sample rapidly, and alert the user to the detection of a concentration of the gas that exceeds a predetermined threshold level.
A well developed approach to detection of hazardous gases uses colorimetric indicators. With this approach, certain chemicals are used as indicators of a level of concentration of a particular gas. These chemicals undergo a significant color change when exposed to a particular gas. Colorimetric indicator reactions are employed in present detection devices by providing personnel who work in locations having the potential for exposure to certain target gases with badges that can hold strips of paper impregnated with a chemical colorimetrically sensitive to the specific target gas. These badges are then worn by the personnel. Such badges can be designed that are inexpensive to produce and very sensitive to the target gas.
One consideration associated with the use of a badge of this type is exposing the paper in the badge to an adequate supply of the environmental air (this combines the tasks of obtaining a sample of the air in the environment and bringing it into contact with the paper). Another consideration relates to detecting the color change in order to alert the badge wearer of such change.
Some air monitor devices are known in which a light sensor is positioned over the colorimetrically sensitive paper strip to measure the change of color of the paper. In order to eliminate or minimize the effects of extraneous or ambient light while measuring the color change of the paper, these devices have required lenses or collimators positioned over the paper. This causes the monitors to be bulky and inconvenient to wear and use. Another consideration related to positioning a sensor over the colorimetric material is that the sensor should not interfere with the exchange of air between the material and the ambient environment.
Some previous devices use a pump or other means to move the air into contact with the strip. This however also increases the size, weight, and bulk of the device and further requires the provision of a power source to operate the pump.
Accordingly, with these concerns and others taken into consideration, it is an object of the present invention to provide a gas monitor badge in which the wearer can be readily alerted to an exposure to a hazardous gas.
It is another object of the invention to provide a monitor device that can be worn readily by personnel in areas where there is potential for exposure to hazardous gas.
It is another object of the present invention to provide a monitor for the exposure to hazardous gases that minimizes power source requirements.
In addition to above concerns, a further consideration of increasing significance in the monitoring of exposure to hazardous gases in a working environment relates to monitoring of exposure duration. Standards for exposure to certain gases are in some cases considered in terms of not just a single instantaneous exposure threshold level, but rather in terms of a cumulative exposure to a level over a period of time.
Accordingly it is also an object of the present invention to provide a gas exposure monitor that measures exposure to one or more certain target gases over a period of time.